Deep brain stimulation is a therapeutic technique involving implanting a medical appliance known as a cerebral stimulator that sends electrical impulses to specific portions of the brain. As an example, stimulation of the thalamic nucleus or the hypothalamus may be used to treat motor disorders such as tremor, caused in particular by Parkinson's disease, while stimulation of the subgenual cingulate cortex is in experimental use in the treatment of particularly severe forms of clinical depression that are resistant to treatment.
In all circumstances, a deep brain stimulation intervention comprises insertion into the cranium of the patient of a flexible lead guided by a cannula and/or a rigid stylus, until the tip of said lead reaches the region of the brain to be stimulated. Using a real time imaging procedure (especially nuclear magnetic resonance), coupled with electrophysiological exploration, means that the moment when the target region of the brain has been reached by the tip of the lead can be ascertained precisely. At this point, the insertion operation is halted, the stylus and/or the cannula are withdrawn from the lead, which is itself locked using a securing device that can ensure that it is held in place for a period that can attain several years.
The document “Medtronic—DBS™ Lead Kit for Deep Brain Stimulation 3387 3389—Implant Manual” from Medtronic Inc, which can be downloaded from the following website: http://www.medtronic.com/physician/activa/downloadablefiles/197928 b 006.pdf describes leads for deep electrical neurostimulation and a method of implanting them.
That document also describes a securing device comprising a part in the form of a sleeve for inserting into a cranial opening produced by craniotomy, and a cap that can be engaged with the sleeve to seal that opening. The sleeve-shaped part includes a collar that is intended to rest on the outer surface of the patient's cranium and that has radially oriented grooves. To secure an implanted lead using such a device, it is necessary to bend the proximal end (i.e. leaving the cranium) of said lead by about 90° and to introduce it into one of said grooves where it is kept in place by the cover.
Under such conditions, the operation of securing the lead has a tendency to cause small involuntary movements of its tip inside the patient's brain. Since the dimensions of the target regions that are to be stimulated are of the order of a few millimeters, such movements can considerably reduce the efficiency of stimulation.
Document U.S. Pat. No. 7,302,298 describes a deep brain stimulation lead kept in place by a screw thread that is introduced directly into an opening formed in the patient's cranium. That securing method suffers from the considerable drawback of causing rapid degradation of the passivation coating of the lead.